This invention relates to linear motor elevators, and more particularly to linear motor elevators by which an elevator car is hoisted up and down by means of a linear synchronous motor within a hoist way (shaft).
FIG. 2 is a schematic perspective view of a ropeless linear motor elevator which has recently been developed. On the interior side walls of a hoist way 1 are disposed a multitude of primary side coils 2, which are arranged repeatedly in the order of U-, V-, and W-phases. For simplicity, FIG. 2 shows only one of the primary side coils 2.
The hoisted body or elevator car 3 hoisted within the hoist way 1 is provided on both sides thereof a plurality of rows of permanent magnets 4, which oppose as the secondary side magnets the primary side coils 2 of the linear motor. Each horizontal row of permanent magnets is divided into four magnet parts 4a through 4d, two each being fixed to the right and left side walls of the elevator car 3. In each row, the magnets 4a through 4d are attached on the elevator car 3 in such a manner that the polarities of the third magnet 4c and the fourth magnet 4d agree with those of the first magnet 4a and the second magnet 4b, respectively. As shown in FIG. 2, the polarities of the first magnet 4a and the second magnet 4b are opposite, and the polarities of the permanent magnets 4 alternate in each column (i.e., vertically).
The primary side coils 2 are each coupled to a power source at the center thereof. A linear synchronous motor is constituted by the primary side coils 2 and the permanent magnets 4 mounted on the elevator car 3. Each one of the primary side coils 2 forms a loop which is twisted 180 degrees at positions between the first magnet 4a and the second magnet 4b and between the third magnet 4c and the fourth magnet 4d. Thus, the linear motor is the null-flux type, and the primary side coils 2 also serve as a guide means for guiding the elevator car 3 in the X- and Y- directions.
The method of operation of the linear motor elevator of FIG. 2 is as follows. Upon receiving a start command signal, a converter device (not shown) such as the VVVF device supplies an excitation current to the primary side coils 2. The primary side coils 2 are excited and a magnetic field moving vertically along the hoist way 1 is generated. The thrust or the driving force generated by the linear synchronous motor along the Z-axis hoists the elevator car 3 up and down along the hoist way 1.
When the elevator car 3 reaches a destination floor 5, the excitation current supplied from the converter to the primary side coils 2 is shut off and the elevator car 3 is stopped by means of a breaking device (not shown).
If the elevator car 3 is displaced in the X- or the Y-direction during hoisting, a circulating current which offsets the variation of the magnetic flux entailed by the displacement of the elevator car 3 flows through the primary side coils 2. Thus, a force is generated which adjusts the elevator car 3 to the central position within the hoist way 1. This compensation for spatial displacement is referred to as the null-flux method. Accordingly, the primary side coils 2 serve not only for hoisting the elevator car 3 but also for guiding the elevator car 3 in the horizontal directions.
The above recently-developed null-flux type ropeless linear motor elevator has the following disadvantage.
(a) The forces acting on the elevator car 3 include not only the driving force along the Z-axis but also subsidiary forces, including, in particular, the strong attractive forces along the Y-axis. Thus, the elevator car 3 must be provided with sufficient structural strength for endure these strong attractive forces with a safe margin. As a result, the elevator car 3 becomes heavy.
(b) Further, only one side of the permanent magnets 4 is utilized effectively for generating the driving force. Thus, the permanent magnets 4 become heavier.
(c) As a result of (a) and (b), the linear synchronous motor and the associated devices therefor, such as the power source and the converter, become large. The overall dimension of the linear motor elevator thus becomes large and the installation cost increases.
(d) In addition, the consumption of power is excessive.
(e) The permanent magnets 4 are fixed directly on the side walls of the elevator car 3. This makes the production and the installation of the elevator car 3 difficult to perform.